The detergents used in mechanical dishwashers usually are in the form of powders, granulates, or tablets. The feeding devices in these machines, into which the detergents are filled before washing, are constructed to accommodate solid products and normally consist of closable chambers that open during the main wash cycle to release their contents. A number of disadvantages result from this method of operation. When the detergent is poured in, the user must tap the storage package or the measuring cup to make the powder flow into the feed chamber, which frequently leads to the spilling of relatively large quantities of the powder and/or to contact with the skin. These spilled portions usually are lost for the washing operation since they are siphoned off at the end of the pre-wash cycle, together with the cold pre-wash liquor. Also, if powder gets into the opening mechanism of the feed chamber during filling, the cover may not close completely or the magnetic closure or mechanical/electrical closure used in some constructions may not lock securely enough, so that part or all of the powder seeps out when the loading door of the dishwasher is closed and is again lost for the main wash cycle. Problems can also arise in machines in which the feed chamber is additionally secured with a protective screen and detergents are used that do not have an optimal rate of solution or have become lumped together during standing for an extended time in opened cartons. A detergent that is incompletely dissolved during the wash cycle results in poorer cleaning and impairs the action of the acid rinsing agent. Also, conductivity measurements have shown that readily soluble detergents require a relatively long time--under unfavorable circumstances up to 10 minutes--for complete solution following their release, which means that the operation proceeds for a considerable length of time with a low concentration of detergent. Improvements attempted during recent years concerning the machine, the rinsing-in mechanism, and the detergents, have been directed to improvements in the free flow and faster rate of solution for the always solid detergent. The possibility of using liquid agents has been limited to the acid rinsing product, which is usually filled into a storage container.
The use of liquid detergents rather than powders in dishwashers has not been considered since the widely used feeding devices are not suitable for liquid agents as presently constructed. Also, there has been the expectation that a storage tank comprising an integral part of the machine would warm up considerably during each wash cycle and lead to the decomposition of the source of active chlorine normally included in the detergent.